1. Field of the Invention
The present invention relates to a fitting for fuel tanks which is intervened between a fuel tank and a pipe.
2. Description of the Related Art
Conventionally, rubber hoses have been intervened between a resinous filler pipe, which is communicated with a filler opening, and a fuel-tank fitting, which is installed to a fuel tank. Recently, a fuel-tank fitting has been developed which is connected directly with a filler pipe, for example, one which is disclosed in Japanese Unexamined Patent Publication (KOKAI) NO. 2002-54,519. FIG. 13 illustrates an axial cross-sectional view of the fuel-tank fitting set forth in the publication. As shown in the drawing, a fuel-tank fitting 100 comprises a fitting body 101, a flange 102, and a check valve 103. The fitting body 101 comprises a projection 107, and an accommodation 108. The projection 107 protrudes to the outside of a fuel tank 106. A connecting end 104 is disposed at the leading end of the projection 107. The connecting end 104 is fitted into a filler pipe 105 by press-in fitting. The flange 102 is formed to have a diameter enlarging from small to large in a direction away from the root of the projection 107. The flange 102 is welded to the opening periphery of an installation opening 109. The check valve 103 is disposed in the accommodation 108. The check valve 103 opens only in a direction heading from the outside of the fuel tank 106 to the inside.
In the fuel-tank fitting 100, it is necessary to secure a fuel-sealing ability between the projection 107 and the filler pipe 105. However, the resinous filler pipe 105 exhibits a lower configuration-following ability than that of rubber hoses. Therefore, it is needed to provide the projection 107 fitted into the filler pipe 105 with a larger press-in allowance in order to secure a reliable fuel-sealing ability. That is, it is required to lengthen the projection 107.
When the projection 107 is made longer, stresses might concentrate at the root of the projection 107 if certain shocks are applied to the projection 107 or the filler pipe 105. Accordingly, there arises a fear that cracks “a” and “b” occur, for example. When the cracks “a” and “b” occur, the inside and outside of the fuel tank 106 are communicated with each other. Consequently, a fuel has leaked out of the fuel tank 106. Thus, it is feared that the fuel-tank fitting 100 might not secure a satisfactory fuel-sealing ability for the fuel tank 106 upon being subjected to shocks.
On the other hand, the thickness of the fuel-tank fitting 100 can be enlarged to upgrade the shock resistance in order that the fuel-tank fitting 100 secures an adequate fuel-sealing ability for the fuel tank 106. However, when the fuel-tank fitting 100 is thickened, it is difficult to carry out the molding. That is, the molding cycle has been prolonged, for instance. Moreover, there is a fear that molding shrinkage might result in the occurrence of sink marks.